Dashpot



W. MAYALL Oct. 3.1, 1961 DASHPOT Filed Dec. 17, 1958 INVENTOR WILL/AM MAY/ILL 5 ATTORNEYS United States Patent 3,006,440 DASHPOT William Mayall, 215 St. Clair Blvd., Hamilton, Ontario, Canada Filed Dec. 17, 1958, Ser. No. 781,074 7 Claims. (Cl. 188-96) This invention relates to a dashpot of the kind having a piston which is relatively unconstrained against movement in one direction, and which is constrained to return in the opposite direction in a controlled manner and at a determined rate.

Prior dashpots of this kind have included a cylinder containing a fluid and a piston which is movable longitudinally within the cylinder and which is in sealing engagement with the bore thereof, the piston or cylinder being provided with a valve-controlled transfer port which permits a relatively unrestricted flow of fluid from one side of the piston to the other in one direction, and which imposes an appreciable frictional drag on the fluid flow in the opposite direction. In these dashpots the piston has been positively moved in one direction against the bias of a spring which is employed to effect the return of the piston to its initial position.

An object of the invention is to provide a dashpot in which the need to provide valve means controlling the transfer of the dashpot fluid is obviated, and in which the return of the piston is effected without the aid of springs or like devices.

Another object of the invention is to provide a dashpot of extremely simple and inexpensive construction in which the need to provide for sealing engagement between the piston and the cylinder wall is obviated.

According to the invention, the dashpot comprises a container for a liquid, a quantity of liquid within and partially filling the container, and a piston within the container and movable for it to be submerged in the liquid, the piston being spaced from a side wall of the container and being of a density which is less than that of the liquid so that the piston will float relatively to the liquid, the piston having an internal cavity which is open at an upper surface of the piston to permit the liquid to flow freely into the cavity when the piston is submerged and having a perforation located at a position below said upper surface and which communicates with the cavity, and operating means acting on the piston for forcing the piston downwardly into the liquid, the combined weight of the piston and operating means being less than the weight of liquid displaced by the piston when the piston is submerged in the liquid to a position in which the internal cavity is filled with liquid, whereby the piston and operating means will be displaced upwardly by the liquid in a controlled manner and at a predetermined rate when such movement is permitted by the operating means.

Further objects and advantages of the invention will become apparent from a study of the following specification, when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic perspective view showing the dashpot of the invention in the environment of an escapement mechanism of a towel dispensing device, such as is disclosed in my co-pending United States patent application Serial No. 793,432, filed February 16, 1959.

FIGURE 2 is a longitudinal sectional elevation through the dashpot of FIGURE 1;

FIGURE 3 is a longitudinal sectional elevation corresponding to FIGURE 2, and showing a modified form of piston assembly;

FIGURE 4 is a longitudinal sectional elevation corresponding to FIGURE 2, and showing another form of piston assembly;

FIGURE 5' is a longitudinal cross-sectional elevation corresponding to FIGURE 2, and showing still another form of piston assembly; and,

FIGURE 6 is a longitudinal cross-sectional elevation through another form of dashpot according to the invention.

In FIGURE 1 the dashpot of the invention is indicated generally at 10, the dashpot, as will be seen more clearly from FIGURE 2, comprising a cylindrical container 11, a quantity of liquid 12. partially filling the container, and a piston 13. A piston rod 14 is secured to the piston 13 and extends vertically upwardly of the piston through a tubular guide 15a fast with a closure 15 of the container.

The guide 15a extends downwardly into the container for a distance which is greater than the depth of liquid in the container, and is so spaced from the wall of the container that in the event of the dashpot being inverted, for example, during transit, the liquid will collect in the annular space between the container wall and the guide 15a and its egress from the container will be prevented. In this way the liquid is prevented from escaping from the container, while at the same time the need for providing packing glands or the like between the guide 15a and the piston rod 14 is obviated. Also, the piston rod 14- is free to pass through the guide 15a in an unconstrained manner.

'The piston 13 is arranged with its longitudinal axis substantially vertical and is in the form of a hollow cupshaped member comprised by a horizontal bottom wall 13a and a peripheral side wall 13b which extends upwardly of the wall 13a and which is spaced from the juxtaposed cylindrical side Wall of the container 11, the horizontal wall having a perforation through which the fluid 12 has access into and from a cavity 130! defined by the walls 13a and 13b of the piston. The perforation 13c is of a cross sectional area selected to obtain a predetermined fiow of liquid therethrough.

In FIGURE 1 the dashpot arrangement is shown in the environment of an escapement for a towel dispensing device of the kind disclosed in my above-mentioned copending application, that escapement mechanism comprising a shaft 20 on which a roll 21 of paper towelling is supported, the roll of towelling being an interference fit with the shaft so that any rotary motion of the roll is positively transmitted to the shaft 20.

The shaft 20 is journalled in suitable bearings (not shown), and at one of its ends carries a snail cam 22 with the camming surface of which coacts a blocking member 23, the direction of rotation of the cam being indicated by the arrow 24 in FIGURE 1 as being counterclockwise.

The cam 22 carries a stop 25 which is spaced radially of the adjacent portion of the periphery of the cam by a distance which is slightly in excess of the height of a blocking member 23, so that when the upper edge of the blocking member is in engagement With the start 22a of the camming surface the blocking member may pass freely between the camming surface and the stop 25, whereas if the blocking member is not in engagement with the start of the camming surface the stop 25 will engage the blocking member to prevent rotation of the cam and thus iprevent rotation of the shaft 20 and the roll of towelling "21.

The blocking member is carried by an arm 26 which is supported from a structural member of the mechanism for rocking movement about a pivot 27, and the arm 26 is loosely connected to the piston rod 14 so that when the cam 22 is rotated the blocking member and the arm will be moved downwardly to depress the piston rod 14 of the piston 13 and to force the piston downwardly into the body of liquid within the container.

When the blocking member 23 leaves the end 22b of the rise of the cam it is in a position in which it is engaged 3 by the stop 25 to prevent further rotation of the roll of towelling, and it is not until the blocking member is raised into engagement with the start 22a of the camming surface that the escapement mechanism is freed for a subsequent operation.

The piston 13 is formed to be of a density substantially less than the density of the liquid in the container. This is accomplished by using for the piston a material which is less dense than the liquid; alternatively the piston may be formed with cavitied walls from a material denser than the liquid, as hereinafter described. In the latter case the term density of the piston refers to the average density of the heterogeneous mass which constitutes the piston.

Because of its comparatively low density the piston will normally float on the liquid, while supporting the weight of the piston rod 14 and the weight represented by the moment of the blocking member 23 and arm 26 about the pivot 27. Even when the piston is forced downwardly into the liquid to a position in which its internal cavity 130! is filled with liquid, there will still be a buoyant force tending to displace it upwardly, because the weight of the piston assembly (i.e. the combined weight of the piston and piston rod and weight represented by the moment of the blocking member 23 and arm 26 about the pivot 27) is arranged to be less than the weight of liquid displaced by the piston when the piston is thus submerged.

The dashpot and escapement mechanism functions in the following manner:

flows over the upper edge of that wall to flood the cavity The rise of the camming surface is arranged so that the piston rod is depressed to an extent such that the piston 13 is completely submerged in the liquid 12 at the time the blocking member 23 leaves the terminal portion of the camming surface, at which time the downward force applied to the piston is removed, and the piston is freed to rise in the liquid 12.

Because the weight of the liquid displaced by the immersed piston is greater than the weight of the piston assembly, the piston will rise quickly in the liquid until such time as theupper edge of the Wall 1312 is aligned with the upper surface of the liquid in the container.

As soon as the upper edge of the side wall 13b rises above the level of the liquid in the container, the body of liquid trapped within the cavity of the piston acts to increase the weight of the piston assembly and thus to reduce the difference between that weight and the weight of liquid displaced by the piston. However, the weight of liquid displaced by the piston is still greater than the now enlarged Weight of the piston assembly. Therefore the piston will continue to rise, decreasing the weight of liquid displaced thereby, until such time as the weight of liquid displaced by the piston becomes equal to the weight" of the piston assembly, and the piston will initially assume a position such that these two weights are equal.

However, at this time, the level of the liquid trapped within the cavity is above the level of the liquid in the container, and the liquid in the cavity commences to flow through the perforation 13c at a rate controlled by the viscosity of the liquid and the frictional drag imposed on ;t he flow by the perforation 13c.

i As the liquid in the cavity flows through the perforation 130 the weight of the piston assembly is progressively decreased, and thus the difference between the weight of the piston assembly and the weight of the liquid displaced by the piston is progressively increased, thus causing the piston to rise in the fluid in the container in a controlled manner and at a determined rate dependent on the rate of flow of liquid through the perforation 13c.

It will be noted that thedashpot of the invention does not require a valve for controlling the transfer port provided by the perforation 13c, and also that as the piston is spaced from the container wall the manufacturing tolerances other than the dimensions of the perforation are immaterial.

In the construction of FIGURES l and 2 the liquid is preferably mercury, as in this way the rate of operation of the dashpot can be made almost completely independent of temperature changes. Also, as mercury is subject to oxidation only to a very minor extent and does not evaporate, the level of the liquid in the container is maintained constant without the need for providing elaborate sealing devices. Thepiston 13, which may be considered to be a float, may be formed of metal, in which case the metal is preferably lacquered to prevent amalgamation between the mercury and the metal, but is preferably formed from a close grained Wood or a moulded plastics material.

Various other liquids are available which meet the requirements of low change in viscosity due to temperature change, negligible evaporation, and insusceptibility to oxidation. One such liquid falling into this class is ethylene glycol, and this liquid may conveniently be used in place of mercury by modifying the structure of FIGURES 1 and 2 in the manner shown by way of example in FIG- URES 3 to 5.

In FIGURES 3 to 5, the only difierence in structure between that of FIGURES 1 and 2 is that the piston walls are cavitated or are formed from a material having a very low density, to obtain the necessary diiference in density between the piston and the ethylene glycol so that the piston even when submerged will fioatably support the weight of the piston assembly.

In FIGURE 3 the piston is shown, for example, as being formed of two cup-shaped members 30, 31, one of which is fitted within the other and which are secured together in sealing relationship at the free edge of their peripheral side walls to define a sealed cavity 32. The members 30 and 31 may be formed from metal sheet or foil or any other light weight substance compatible with the ethylene glycol and are provided with aligned apertures to provide the necessary perforation 33.

In FIGURE 4 the piston is shown as comprised by a ring 40 of cork or of a foamed plastics material which is sheathed in a liquid impervious film 41, and which is attached to a disc 42 having a perforation 43,. the disc pro viding a bottom wall of the piston,

. In FIGURE 5 the piston is shown as being a moulding 1 50 of a foamed plastics material which is perforated at 51 and which is sheathed with a suitable liquid impervious film 52.

The operation of each of the dashpot assemblies shown in FIGURES 3-5 is identical to that described with reference to FIGURE 2 in all respects.

It will be noted that in the construction of each of FIGURES 2-5 the piston is guided for substantially vertical movement by the randomengagement of its rod 1 in the bore of the guide 15a.

'In certain conditions it 'may be desirable that the piston rod is not attached to the piston, for example, it may be necessary to accommodate free movement of the piston rod, in which event recourse may be had to the construction shown in FIGURE 6.

In FIGURE 6 the piston 60 is guided by the arms 61 of a spider placed in or formed integrally with the cylinder 62, the arms of the spider guiding the piston for substantially vertical movement while at the same time pro- 'viding a free space around the periphery of the piston through which the liquid can pass upwardly for it to flow into'the cavity of the piston. In this casethe piston rod is a rigid member 63 of any convenient configuration which engages the interior surface of the bottom of the piston but is not attached thereto. It will also be noted that in FIGURE 6 the piston is shown as having the form of a thimble provided by a tube which is closed at one end and which is provided with the necessary perforation 64.

It will be appreciated that the various modifications of construction shown in the drawings are to be taken by way of example only of the many forms the dashpot assembly of the invention may take, and that various other constructions are possible without departing from the scope of the invention defined by the appended claims.

What I claim as my invention is:

l. A dashpot, comprising a container for a liquid, a quantity of liquid within and partially filling the container, a piston within the container and arranged to move up and down with its longitudinal axis substantially vertical, the piston being of less density than the liquid and having a side wall which is spaced from a juxtaposed side wall of the container, the piston having an internal cavity which is open at an upper surface of the piston to permit the liquid to flow freely into the cavity when the piston is submerged and having a perforation located at a position below said upper surface and which communicates with the cavity, and operating means acting on the piston for forcing the piston downwardly into the liquid, the combined weight of the piston and the operating means being less than the weight of liquid displaced by said piston when said piston is submerged in said liquid to a position in which the internal cavity is filled with liquid, whereby the piston and operating means will be displaced upwardly by the liquid when such movement is permitted by said operating means.

2. A dashpot, comprising a container for a liquid, a quantity of liquid within and partially filling the container, a piston arranged to move up and down within the container, the piston being of less density than the liquid and having a side wall spaced from a juxtaposed side wall of the container, the piston including a tube arranged with its longitudinal axis substantially vertical and providing the side wall of the piston and a closure for a lower end of the tube for the interior of the tube to define a cavity, the tube being open at an upper end thereof to permit the liquid to flow freely into the cavity when the piston is submerged, a rigid member acting on the piston and operable for forcing the piston downwardly into the liquid, the piston having a perforation located at a position below the open upper end of the tube and which communicates with the interior of the tube, and a. guide associated with the piston and guiding the piston for movement upwardly and downwardly within the container, the combined weight of the piston and rigid member being less than the weight of liquid displaced by said piston when said piston is submerged in said liquid to a position in which the internal cavity is filled with liquid whereby the piston and rigid member will be displaced upwardly by the liquid when such movement is permitted by said rigid member.

3. A dashpot, comprising a container for a liquid, a quantity of liquid within and partially filling the container, a piston arranged to move up and down within the container, the piston being of less density than the liquid and having a side wall which is spaced from a juxtaposed side wall of the container, the piston including a tube arranged with its longitudinal axis substantially vertical and providing the side wall of the piston and a closure for a lower end of the tube for the interior of the tube to define a cavity, the tube being open at an upper end thereof to permit the liquid to flow freely into the cavity when the piston is submerged, a piston rod acting on the piston and operable for forcing the piston downwardly into the liquid the piston having a perforation located at a position below the open upper end of the tube and which communicates with the interior of the tube, and a guide associated with the piston rod and guiding the piston rod and piston for movea a 6 a ment upwardly and downwardly within the container, the combined weight of the piston and piston rod being less than the weight of liquid displaced by said piston when said piston is submerged in said liquid to a position in which the internal cavity is filled with liquid whereby the piston and piston rod will be displaced upwardly by the liquid when such movement is permitted by said piston rod.

4. A dashpot, comprising a container for a liquid, a quantity of liquid within and partially filling the container, a piston arranged to move up and down within the container, the piston being of less density than the liquid and having a side wall which is spaced from a juxtaposed side Wall of the container, the piston including a cup-shaped member arranged with its longitudinal axis substantially vertical for a bottom wall of the cup to lie in a substantially horizontal plane, and for a peripheral side wall of the cup to extend upwardly from said bottom wall for the interior of the cup-shaped member to define a cavity, a rigid member acting on the piston and operable for moving the piston to submerge it in said liquid and to cause the liquid to flow freely around the peripheral side wall and into the cavity as the piston is so submerged, the piston having a perforation located in its bottom wall communicating with the interior of the cup-shaped member, and a guide associated with the piston and guiding the piston for upward and downward movement within the container, the combined weight of the piston and rigid member being less than the weight of liquid displaced by said piston when said piston is submerged in said liquid to a position in which the internal cavity is filled with liquid whereby the piston and rigid member will be displaced upwardly by the liquid when such movement is permitted by said rigid member.

5. A dashpot comprising a container for liquid, a quantity of liquid within and partially filling the container, a closure member for the container and having a hole therein, and a piston assembly, the piston assembly including a piston within and spaced from a side wall of the container and movable for it to be submerged in the liquid, the piston being of a density less than that of the liquid, the piston having an internal cavity which is open at an upper surface of the piston to permit the liquid to flow freely into the cavity when the piston is submerged and having a perforation located at a position below said upper surface communicating with the cavity, the perforation being of cross sectional area selected to obtain a predetermined flow of liquid therethrough into and from the cavity, the piston assembly also including a piston rod supported by the piston for forcing the piston downwardly into the liquid, the piston rod extending upwardly from the piston through the hole in the closure member, and a member acting on the upper end of the piston rod to depress said piston rod, the weight of the piston assembly being less than the weight of liquid displaced by the piston when the piston is submerged in the liquid to a position in which the internal cavity is filled with liquid, whereby, when the piston is thus submerged, the diiference between the weight of the liquid displaced by the piston and the weight of the piston assembly will act on the piston to raise it upwardly in the liquid, the liquid trapped in the cavity of the piston when the upper surface rises above the level of the liquid in the container acting to increase the weight of the piston assembly and retard further upward movement of the piston, the liquid in the cavity then flowing under gravity through the perforation of the piston due to the difference between the level of the liquid in the cavity and that in the container to progressively decrease the weight of the piston assembly and thus increase the difference between the weight of the piston assembly and the weight of the liquid displaced by the piston at a rate controlled by the viscosity of the liquid and the restriction on the flow of liquid from the cavity imposed by the perforation, thus causing the piston assembly to be displaced upwardly by the liquid in a controlled manner and at a determined rate.

6. A dashpot according to claim 5' and having a guide restricting movement of the piston to movement in a substantially vertical plane.

7. A dashpot according to claim 6 in which the piston is of cup-shape, and in which the perforation extends 5 through a bottom Wall of the cup-shaped piston.

References Cited in the file of this patent UNITED STATES PATENTS 598,386 Noble Feb. 1, 1898 10 632,299 Whitaker Sept. 5, 1899 667,652 De Vilbiss Feb. 5, 1901 

